Typical mobile communication systems have been developed to provide voice services while guaranteeing user mobility. Such mobile communication systems have gradually expanded their coverage from voice services through data services up to high-speed data services. However, as current mobile communication systems suffer resource shortages and users demand even higher-speed services, development of more advanced mobile communication systems is needed.
To meet this demand, the 3rd Generation Partnership Project (3GPP) has been working to standardize technologies for various radio access networks (RAN) such as E-UTRAN, UTRAN and GERAN.
Communication systems based on 3GPP standards may support various types of services and terminals. For example, they may support not only communication terminals directly used by persons such as smartphones but also Internet of things (IoT) terminals operable with little or no human intervention. They may also support voice services, multimedia services, device management services, and communication services for delivering specific information to terminals or collecting specific information from terminals.